Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable()
From: Michal Hocko
Date: Tue Jul 11 2017 - 02:50:58 EST
On Tue 11-07-17 08:26:40, Vlastimil Babka wrote:
> On 07/11/2017 08:03 AM, Michal Hocko wrote:
> > On Tue 11-07-17 09:58:42, Anshuman Khandual wrote:
> >>> here. This is hardly something that would save many cycles in a
> >>> relatively cold path.
> >> Though I have not done any detailed instruction level measurement,
> >> there is a reduction in real and system amount of time to execute
> >> the test with and without the patch.
> >> Without the patch
> >> real 0m2.100s
> >> user 0m0.162s
> >> sys 0m1.937s
> >> With this patch
> >> real 0m0.928s
> >> user 0m0.161s
> >> sys 0m0.756s
> > Are you telling me that two if conditions cause more than a second
> > difference? That sounds suspicious.
> It's removing also a call to get_unmapped_area(), AFAICS. That means a
> vma search?
Ohh, right. I have somehow missed that. Is this removal intentional? The
changelog is silent about it.